Needle specifications are written as gauge × length. On a HENDARI 1 mL syringe that reads 31G × 5/16″ (0.25 mm × 8 mm). Here is what each number controls.
Gauge: thickness
Gauge is inverse — the higher the number, the thinner the needle. 31G is at the fine end, with an outside diameter of about 0.25 mm. Fine needles are used where the smallest possible opening matters and where a gentle, controlled flow is wanted.
Length: reach
5/16″ is 8 mm. Short needles keep the tip close to the surface you are working on, which is useful when you are drawing from a shallow vial or dispensing into a small recess.
The combination
31G × 8 mm is the fine-and-short pairing: a small opening, a short reach, and a 1 mL barrel behind it. That is why the same specification shows up in labs, in precision craft work and anywhere a millilitre needs to go somewhere specific.
Handling a fine needle
A 31G tip bends if it is levered sideways. Keep the syringe in line with the needle when drawing and dispensing, cap it by sliding the cap on rather than pushing it on, and dispose of it after one use.